Blue Star Ferries serves a connection to Paros throughout the year. Although the respective timetables will be published on short notice, you can assume that both in winter as well as summer the connection is served by two ships per day. In the summer months, Blue Star Ferries runs a additional connection to Paros from Rafina.
Tips for Blue Star Ferries: Super Economy is the cheapest rate, not Economy.
In the summer, the ships of Hellenic Seaways and Seajet also serve this connection.
For all shipping lines you can buy the tickets online, but you have to collect the tickets in one of the port offices. Only Hellenic Seaways is offering self-printable tickets.